1. Field of the Invention
This invention relates to a linear motion rolling contact bearing assembly, and, in particular, to a linear motion rolling contact bearing assembly having a double row runway structure.
2. Description of the Prior Art
A linear motion rolling contact bearing assembly is well known in the art and it generally comprises an elongated bed or rail extending straight over a length, a table which straddles the straight rail and a plurality of rolling members interposed between the table and the rail, thereby allowing the table to move along the straight rail. In such a prior art linear motion rolling contact bearing assembly, the rail is typically comprised of a relatively thick steel plate which is formed by bending the thick steel plate so as to have a U-shaped cross section with a guide groove, serving as a runway, being formed on each outer side surface of its vertical walls. The rail thus formed to have a U-shaped cross section is set in position with its open side directed upward; and the table is structured, typically from a thick steel plate, to straddle the rail by transversely extending across the open side of the rail.
Such a prior art linear motion rolling contact bearing assembly is relatively high in rigidity as well as in accuracy; however, it is heavy in weight so that it is often the case that a deterioration in the accuracy of positioning is encountered if the bearing assembly is used in a high speed condition because the inertia can become significantly large. Besides, the prior art device is relatively expensive because it requires machining of a thick steel plate at high accuracy in manufacturing.